Given that juries can generally always consider lesser charges, I'm not persuaded.
Certainly. It's a decision by the prosecution. They can go for one charge, and only try to prove that charge - or go for lesser charges as well, and prove the elements of all potential charges. Generally, a prosecution is going to want to get a conviction on something, so will include the lesser charges. In the Zimmerman trial, the prosecutors only attempted to prove the element of the murder charge. They did not include lesser charges, or attempt to prove the elements of any lesser charges. IIRC further, the jury inquired about lesser charges, and the judge rightly told them that they could only consider the charge presented to them.
The statement I saw said he has changed the charge to M2, not added the charge to the existing charge.